Chapter 5

1. Chapter 5 Atomic Structure and the Periodic Table

2. Just How Small is an Atom? You don’t need to write. • A penny contains about 2.4 × 1022 atoms. • A speck 0.1 mm in diameter (about half the size of a period at the end of the sentence) requires one million atoms. • It would require a million atoms, edge to edge, to match the thickness of a page of paper.

3. History of the Development of Atomic Models • Democritus (400 B.C.) • 1st suggested matter is made of atoms • atom- means “indivisible”

4. John Dalton You don’t need to write. • John Dalton (1766-1844), was an English schoolteacher. • Performed experiments to test his atomic theory. • Formulated hypothesis and theories to explain his observations.

5. History of the Development of Atomic Models B. Dalton (1766-1844) Dalton’s Atomic Theory • All elements are composed of tiny indivisible particles called atoms Is this still true? YES

6. Dalton’s Atomic Theory Is this still true? atoms of the same element can have different masses (isotopes) 2. Atoms of same element are identical. The atoms of any one element are different from those of any other element.

7. Dalton’s Atomic Theory 3. Atoms form compounds by combining in whole number ratios Is this still true? • YES: Law of Definite Proportions

8. Dalton’s Atomic Theory 4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element can never change into another element. Is this still true? No, These changes CAN occur in nuclear reactions!

9. Structure of the Atom • Electron Cloud: • -contains electrons • -takes up most of space • Nucleus: • contains protons and neutrons • takes up very little space

10. Discovery of Nucleus C. Rutherford (1871-1937) discovered the nucleus by shooting alpha particles (have positive charge) at a very thin piece of gold foil • he predicted that the particles would go right through the foil at some small angle

11. Discovery of Nucleus

12. Discovery of Nucleus • some particles (1/8000) bounced back from the foil • this meant there must be a “powerful force” in the foil to hit particle back Predicted Results Actual Results

13. Subatomic Particles D. J.J. Thomson (1856-1904) – discovered electrons in atoms; his model was of a positive sphere with e- embedded in it. E. Milliken (1868-1953) found the mass of the electron F. Goldstein found protons in 1886 G. Chadwick (1891-1974) found the neutron

14. Discovery of Electron You don’t need to write. • resulted from scientists passing electric current through gases to test conductivity • used cathode-ray tubes • noticed that when current was passed through a glow (or “ray”) was produced

15. Discovery of Electron This led scientists to believe there were negatively charged particles inside the cathode ray

16. Properties of Subatomic Particles

17. How to find: • # of protons = atomic number • # of neutrons = rounded mass # – atomic # • # of electrons = # of protons

18. Chemical Symbols • Printed: 1st letter capital, 2nd letter lower case • Represents one atom of an element Fe Cl B

19. 2. Important principles about the atom • All atoms are electrically neutral (p+ = e-) • Nearly all mass is in the nucleus • Lots of space between nucleus and e- • Every atom of the same element has the same # of p+

20. 3. Atomic Number is the # of p+ 6 6 15 15 79 79

21. 4. Mass Number is the # of p+ + n0 C Element Symbol Mass Number 12 6 Atomic Number

22. Isotope of an element- same # p+, different # of n0 (Same atomic #, different mass #) 6. Atomic mass unit (amu)- defined as 1/12 of the mass of a Carbon-12 atom

23. Parentheses Indicate Mass of Most Stable Isotope Back to Main Page 7. Atomic Mass- mass averaged of all the isotopes of an element.

24. Mass Number 8. Isotopic Name: Carbon-12 or Carbon-14 a. b. Hydrogen-3 c. Magnesium-27 p+ e- n0 10 21 Ne 10 10 11 p+ e- n0 1 1 2 Mg 27 12

25. Isotope Lab Avg. mass = Mass (of that type of veggie) # of pieces of that type of veggie % abundance = # of pieces of that veggie × 100 Total # of pieces of all veggies

26. Bell Work 9/21 The nucleus consist of ______ and _______. The ______ number of an atom gives the number of protons. The _____ number gives you how many protons and neutrons are in the nucleus. _________ _________ 23 Na Copper-63 11 _________ Atoms that have the same _______ ________ but different numbers of neutrons are ________ of the same element. Since isotopes have different numbers of neutrons, they have a different _______ ______.

27. C. Nuclear Symbols • Chlorine-37 • atomic #: • mass #: • # of protons: • # of electrons: • # of neutrons: • 17 • 37 • 17 • 17 • 20

28. Nuclear Symbol Examples Cl 35 Mg 17 Number of Electrons Number of Neutrons Number of Protons Mass Number Atomic Number 17 35 17 17 18 27 12 Number of Electrons Number of Neutrons Number of Protons Mass Number Atomic Number 12 27 12 12 15

29. Avg. Atomic Mass Average Atomic Mass • weighted average of all naturally occuring isotopes • on the Periodic Table • round to 2 decimal places

30. Avg. Atomic Mass Average Atomic Mass • EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. 16.00 amu

31. Avg. Atomic Mass Average Atomic Mass • EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. 16.00 amu

32. Avg. Atomic Mass E. Average Atomic Mass • EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. 35.40 amu

33. Example: A sample of cesium is 75% 133Cs, 20% 132Cs and 5% 134Cs. What is the average atomic mass? Answer: .75 x 133 = 99.75 .20 x 132 = 26.4 .05 x 134 = 6.7 132.85 = average atomic mass